Method of making composite metal structure



Jan. 30, 1968 E. l; VALYI 3,365,785

METHOD OF MAKING COMPOSITE METAL STRUCTURE Original Filed Sept. 21, 19642 Sheets-Sheet l FIG-4 J1 INVENTOR. 6/ 4 [ME/W Z WILV/ FIG5 w i gdw ATTORNEY Jan. 30, 1968 vALYl 3,365,785

METHOD OF MAKING COMPOSITE METAL STRUCTURE Original Filed Sept. 21, 19642 Sheets-Sheet 2 FIG- 7 FIG-3 Y INVENTOR. 33 4 35 2 EMERVZ [440 FIG 9%V/z A 7'TOR/VEV United States Patent Ofi ice 3,365,785 Patented Jan.30, 1968 3,365,785 METHOD OF MAKING COMPQSKTE METAL STRUCTURE Emery I.Valyi, River-dale, N.Y., assignor to Olin Mathieson ChemicalCorporation, a corporation of Virginia Original application Sept. 21,1964, Ser. No. 398,127, now Patent No. 3,230,618, dated Jan. 25, 1966..Divided and this application Aug. 30, 1965, Ser. No. 499,128

2 Claims. (Cl. 29420.5)

ABSTRACT OF THE DISCLOSURE A method of making a composite sheetmetal-porous metal structure by embedding a first porous body in asecond porous body of relatively less porosity and metallurgicallybonding the first and second porous bodies to an imperforate metalsheet.

This application is a divisional of copending application Ser. No.398,127, filed Sept. 21, 1964, now US. Patent 3,230,618, which in turnis a division of application Ser. No. 202,612, filed June 14, 1962, nowUS. Patent 3,201,858. The latter application is in turn acontinuation-in-part of application Ser. No. 732,663, filed May 2, 1958,now US. Patent 3,049,795, which in turn is a continuation-in-part ofapplication Ser. No. 586,259, filed May 21, 1956, now abandoned.

This invention relates to porous fabrications and more particularly to apermeable body integrated to a supporting sheet metal structure adaptedto conduct a fluid to the said permeable body for flow and distributiontherethrough.

As brought out in the aforesaid co-pending applications, the subjectmatter thereof was directed to novel features wherein a permeable bodyformed of powdered metal is joined to a supporting metal structure so asto become integral therewith in all areas except where they are formedbetween the permeable and impervious portions of the structure.

The resultant porous fabrication may be utilized advantageously invarious applications. For example, it may be employed in the subsequentmanufacture of gas burners that are intended to provide evenlydistributed heat over large surfaces. In such application a combustiblegas is distributed by the fluid channels to different portions of thepermeable body through which it flows to emanate on the combustion sidethereof substantially uniformly over most of the surface of that body ata substantially uniform rate, thus producing a flame blanket. Theresultant porous fabrication may also be utilized advantageously in theconstruction of evaporative coolers whereby an efficient cooling surfaceis obtained by using the porous metal body as a means through which todistribute over a large area the liquid which is to evaporate for thepurposes of transpiration cooling. In a further application, the porousfabrication may be utilized in the construction of filters wherein theporous metal body provides a controlled porosity and permeability so asto enable a liquid carrier to filter through the porous metal body whileleaving filtrate on the other side thereof. As will be recognized, oneof the most important limitations restricting the use of porousfabrications resides in the fact that it is very diflicult and costly toprovide conduits which conduct fluids efiiciently to the appropriatefaces or portions of the porous metal bodies, and therefrom to bedistributed into and through such porous metal bodies for the purposesof combustion, evaporation, filtration, or other purposes. Anotherlimitation of porous metal bodies restricting their use in componentsdesigned to transfer heat from one medium to another derives from thefact that the heat conduction of such porous bodies is less than that ofsolid metal bodies and that it is ditficult and costly to effectefficient heat transfer to the porous bodies and through them. While thetechniques and methods of producing pervious or porous bodies frompowder metal have been extensively discussed in the literature such asfor example in Powder Metallurgy by Dr. Paul Schwarzkopf (the MacmillanCompany, New York, 1947) and Powder Metallurgy edited by John Wulff (theAmerican Society for Metals, Cleveland, 1942) no economical andeflicient method has been found thus far to overcome the limitationsabove referred to prior to the invention described in the aforesaidco-pending applications; the basic concept of the contribution thereincomprises the forming of an integral structure of two or more metallayers of diflering characteristics, of which at least one layer isporous and pervious to fluids, such as gases or liquids, and the othersimpervious and solid, these layers being secured together, preferablythrough a sintering operation, a though brazing and other means may alsobe employed, so as to enable the formation of fluid channels inpredetermined portions between the confronting faces of various layerscomprising the integrated porous structure.

In accordance with the disclosure of the aforesaid copendingapplications, the porous fabrication is formed from a supporting sheetmetal member which may have all or a portion thereof in the form of afiat, relatively thin plate, sheet, or strip. A pattern ofweld-inhibiting material is applied to this member in a designcorresponding to that desired for the fluid conducting channels whichare to be provided in the ultimate structure. Following the applicationof the weld-inhibiting material, a substantial layer of powdered metalaggregate is deposited upon the plate thus treated. Subsequent theretothis composite structure may be subjected to pressure to compact thepowdered metal and to press it firmly against the solid plate. Thiscompacted assembly is then exposed to a suitable sintering temperatureunder conditions preventing undesired reactions, such as oxidation ofthe metal. This sintering operation accomplishes the sintering of thepowdered metal particles to each other together with the metallurgicalbonding, welding, of the sintered metal aggregate to the solid member.

In an alternate method disclosed in the foregoing conpendingapplication, the powder metal layer may be separately formed by knownpowder metallurgy techniques. In this method the solid sheet metalmember may be first prepared by applying a pattern of weld-inhibitingmaterial to the portions thereof at which the fluid channels are to beformed, and applying to one side of the porous metal layer a suitablethin layer of soldering or brazing metal. The porous metal layer is thensuperimposed upon the solid plate so as to sandwich the Weld-inhibitingmaterial between them, and the composite subjected to a thermaltreatment to accomplish the brazing or soldering of the porous metallayer to the sheet metal member in all adjacent areas thereof except inthose portions separated by the weld-inhibiting material.

The resultant composite structure may now be adapted for the conductingof fluids by deforming or flexing those portions of the sheet metalmember, which are disposed opposite the weld-inhibiting material, awayfrom the porous metal layer. This can be accomplished for example byintroducing a fiuid under pressure into the ununited portions of thecomposite structure formed between the porous layer and a sheet metalmember, or mechanically, by insertion of suitable mandrels into theseareas. This deformation of the sheet metal member away from the porousmetal layer will form fluid channels defined on one side by animpervious metal wall portion and on the other side by the porous metal.

As will be understood, various combinations of materials may be utilizedin forming the integrated composite structure; and accordingly the solidsheet metal member and the porous layer or body may be of the same metalor alloy, or the porous structure and the solid member, of theintegrated structure, may be comprised of different compositions. Forexample, both the porous metal layer and a solid sheet metal member maybe formed of the same stainless steels, coppers, brass, carbon steels,aluminum or various combinations thereof. As will be understood theultimate use of the resultant integrated structure determines thespecific combination of alloys to be employed.

Accordingly, among the objects of this invention is to provide means forfabricating novel porous metal structures adapted to distribute a fluidand heat in flow therethrough.

A further object of this invention is to provide a novel method formaking porous metal structures adapted to distribute a fluid and heat inflow therethrough.

Other objects and advantages of this invention will become more apparentfrom the following drawings and description in which FIGURE 1 is aperspective view illustrating one embodiment of the present invention ina preliminary stage of fabrication;

FIGURE 2 is a perspective view of one embodiment of the presentinvention in a subsequent stage of fabrication;

FIGURE 3 is a perspective view of the embodiment of FIGURE 2 in asubsequent stage of fabrication;

FIGURE 4 is a sectional view along the line lV-IV of FIGURE 3;

FIGURE 5 is a sectional view along the line VV of FIGURE 3;

FIGURE 6 is a perspective view of a related embodiment of the presentinvention;

FIGURE 7 is a sectional view along the line VIIVII of FIGURE 6; and

FIGURES 8 and 9 are sectional views of related embodiments of thepresent invention.

In regard to production of the porous body, it may be obtained by theso-called gravity sintering method which comprises a process whereingraded metal powder, frequently spherical metal powder, is poured bygravity into an appropriately shaped confined space, and usuallyvibrated to cause it to compact uniformly. As is obvious the choice ofparticle size of the metal powder will largely determine the amount ofporosity, i.e., void space. The metal powder or aggregate so packed isthen sintered in accordance with well-known powder metallurgy practices,producing a porous metal body whose bulk density, or apparent density,is but a fraction of the density of the meal or alloy from which thepowder particles are obtained. Generally the conditions of vibration andconditions of sintering are chosen to result in an apparent density ofapproximately 25% to 75% of the solid density of the correspondingalloys. In another procedure for the production of such porous metalbodies the process may comprise blending intimately a graded metalpowder with a combustible substance, such as for example wood flour orother organic particulate material, or a soluble material Whose meltingpoint exceeds the sintering temperature of the metal powder. After theformulation of this dry blend, the mixture of metal powder andcombustible or soluble sustance is then compacted under pressure, suchas by rolling resulting in a body that has no voids and is reasonablyfirm, sufficient for handling. This body is then sintered in accordancewith well-known powder metallurgy practices to produce a cohesivestructure in which the metal particles are sintered together at theirrespective points of contact and the combustible or soluble materialremains unbonded to the metal particles forming discrete islands withinthe metal body. Upon completion of the sintering operation and if thenonmetallic component is combustible, then the resultant body will infact contain void spaces everywhere previously occupied by thecombustible material since the latter will have burned away in thecourse of sintering. In the case utilizing a soluble material whosemelting point is higher than the sintering temperatures of the metal,the soluble material will remain intact after the final stages ofsintering and can be subsequently removed by leaching and dissolvingwith a liquid, resulting in a network of interconnected pores.

In the modification of the foregoing it is noted the above described dryblend of metal powder and combustible or soluble substance may bereplaced, respectively, by a paste or slurry obtained by suspending theadmixed powder metal and combustible or soluble particles in a suitableliquid vehicle, as for example water or alco hol; or in applicationswhere the combustible substance is mostly organic, by choosing acombustible substance that is a viscous liquid instead of beingparticulate such as for example a liquid phenolic resin. Alternately themixture of metal powder and void or pore forming substance and vehicle,or void or pore forming substance alone, may be prepared into a pastewhich may be brought into the desired shape by pressing or extrusion.

A further method of producing the sintered porous metal bodies comprisesmelting a metal or alloy and casting it into the interstices of a porousaggregate of a particulate soluble material whose melting point exceedsthat of the metal. Upon solidification of the metal, a component isproduced which contains the network of the soluble material interspersedwithin the solid metal which soluble material is thereupon removed byleaching or dissolving, leaving behind it interstices that interconnectand form a porous network within the resultant metal body. Solublesubstances contemplated for these purposes, be it for blending withsolid metal powder or for the above casting process, comprise sodiumchloride in conjunction with aluminum and aluminum alloys, aluminumfluoride in conjuction with copper alloys, and calcium oxide inconjunction with alloys having melting points higher than copper alloys.As will be understood other substances, particularly inorganic salts,are readily available and known to the art for such purpose as forexample various phosphates, such as tri-sodium phosphate.

A still further method of producing a porous metal body comprisesweaving or knitting metal wire into a mesh arranged in a plurality oflayers. According to this process, a control of porosity is obtained byappropriate choice of wire diameters and openings arranged betweenadjoining wires as well as the juxtapositioning of superimposed layersof the woven or knit mesh.

Although a specific mass of sinterable metal has been described, it ispointed out that other formulations of sinterable materials may also beused, as for example those metal oxides, carbides and nitrides, ormixtures thereof, containing if necessary pore or interstice formingmaterials discussed above.

Various substances are known to be effective in preventing adhesion ofone metal body to another, even under severe pressure. as in rolling, atelevated temperatures, as in the course of soaking prior to rolling, ordiffusionannealing, etc. In fact, many substances present in metal asaccidental impurities, as for example manganese sulphide in steel,operate to produce seams and other discontinuties in rolled products.Among these substances are graphite, applied for example in the form ofcolloidal suspensions, boron nitride, talcum, zinc oxide, titania, andmany others each within certain limits of applicability that are notrelevant here. In fact, it has been noted that on occasion duringroll-welding of two superimposed sheets interference with theintegration occurs even by the mere presence of an accidental oil smudgeon the surfaces of the sheets. For purposes of the present invention,the separation or weld-inhibiting materials employed need not withstandexposure to high pressures or be capable of extending under pressurewhich normally are requisites of stop-weld resist used in pressurewelding. Instead, the weld-inhibiting material employed as the spacer orsupporting substance herein need only have reasonable mechanicalstrength to function as a spacer or support before the superimposedparticulate material acquires strength of its own as the sinteringoperation progresses. The weld-inhibiting material employed as a spaceror supporting substance should preferably be capable of being applied atroom temperature as a powder or by spraying, painting, extrusion, etc.;if needed, harden with the least time delay, and remain in place throughthe better part of the subsequent operations which usually comprise theapplication of a loose particulate metal layer of transporting thecomposite preparatory to a sintering operation and of sintering.Moreover, this spacer or supporting substance must be capable of removalfollowing the sintering operation even if the channel network isextremely complex and tortuous.

Preferably the spacer for supporting substances contemplated herein areliquid soluble and have a melting point higher than the sinteringtemperature of the particulate metal layer, or at least higher than thetemperature at which that layer commences to acquire reasonablemechanical strength in the course of sintering. Such soluble substancesare for example sodium chloride, which melts at 801 C., a temperaturesomewhat below the customary sintering temperature of copper; and it maybe used in connection with copper aggregate because the latter willacquire adequate strength during sintering before the sodium chloridebegins to melt. Other such soluble substances are sodium aluminate(melting at 1,650 C.), potassium sulphate (melting at 1,076 0.), sodiummetasilicate (melting at 1,088 C.), aluminum chloride (melting at l,040C.), and others. The choice of such soluble spacer or supportingsubstances will of course also depend on possible solid phase reactionswith the metal surrounding them, at the temperatures of sintering. Forexample, while one of the most effective weld-inhibiting materialsadapted for use as the spacer or supporting substance in connection withcopper and aluminum alloys is graphite or carbon, austenitic stainlesssteel would be harmed by that spacer substance through carburizing.

In this respect it is pointed out that also contemplated within thisinvention is the utilization of a specific form of a carbon as aweld-inhibiting material in the fabrication of these compositestructures. The particular form of carbon contemplated is that obtainedin situ. from organic substances, by pyrolysis. As is known, progressiveelevated temperature exposure of a variety of organic substances ininert or reducing atmospheres results in progressive thermal degradationof the organic material and ultimately in pyrolysis similar to coking.The residual carbonaceous matter is strong and cohesive as well asstable, except under oxidizing conditions at elevated temperatures. Theresultant weld-inhibiting material, originally introduced as an organicsubstance may thus maintain reasonable mechanical strength and itsfunctional integrity not only at room temperature but also throughoutthe process of heating during the sintering operation, while the powdermetal acquires appreciable strength and ability to support itself over apreformed channel forming the groove of the desired composite structure.However, the organic material applied to the solid metal surface orwithin the preformed channel of a solid metal member, may be used as aweld-inhibiting material only if the carbonaceous residue remainingafter the sintering operation is removed. This in turn depends upon theparticular metal aggregate applied above it which must be pervious andporous enough to permit the ambient atmosphere to react freely with thecontents of the channels. In such a case, the pyrolized organicsubstance will break down further and oxidize Without residue, if thesintering furnace atmosphere is adjusted to allow for progressiveformation of gaseous carbon compounds, or, as is preferable, if exposedto air while still hot enough to oxidize vigorously.

For example, a paste-like mixture of silica sand and a phenolic Varnishof the resol type may be used. The weld-inhibiting materials so formedcan be hardened at room temperature and then upon exposure to increasingtemperatures, will progressively harden and cure as is naturallyexpected for a phenolic resin, and thereafter progress through severalstages of heat degradation while heated to still higher temperatures inan inert atmosphere. In a specific application in which sperical copperparticles were metallurgically bonded to a copper sheet, during thecourse of the sintering operation the sand particles remained bondedtogether due to the carbonaceous residue of the phenolic resin. Uponremoval of the sintered composite from the furnace and while still at anelevated temperature approaching that of the furnace, but now exposed toambient air, the carbon oxidizing almost instantaneously leaving thesand free flowing and devoid of any bond.

Oxidation of the pyrolyzed residue may be accomplished usually by mereexposure to an atmosphere containing sufiicient oxygen to burn thecarbon, but not enough to oxidize the metal harmfully. In the case ofcopper, sintering may be followed by air exposure at room temperature,as above described; in the case of stainless steels, if brightness is tobe preserved, cooling after sintering may take place in a protectiveatmosphere which may have just enough oxygen to react with the carbon. Awide variety of such weld-inhibiting spacer and supporting substancesare readily avilable and known to the art; and in principle suchformulations usually consist of freefiowing comparatively inert granularmaterials, such as silica sand, bonded with phenol formaldehyde,ureaformaldehyde, polystyrene, polyethylene, furfural formaldehyde, coaltar, etc., or such organic materials alone and others for example,paper, adhesive tape, etc, in the event that only thin films need to besupplied prior to sintering.

In accordance with an embodiment of this invention shown in FIGURE 1,these porous composite structures can be formed without deforming thesheet metal member. In accordance with one modification of thisembodiment a first body 59 representing a sinterable permeable structureof relatively coarse porosity is provided on a face of a sheet metalmember 60. Thereafter this first porous body is then encased Within asecond permeable body 61 superimposed on the same face of sheet metalmember 60 with this second body having pores relatively finer than thatof the first permeable body. The components of the resulting structurecan be joined by sintering or in accordance with any of the abovedescribed joining methods. As a result a composite structure is formedwhich, in substance, comprises three layers as illustrated in FIGURE 2,namely a solid sheet metal component 60, a first pervious component 59,and a second porous component 61. The first pervious component 59 ischaracterized primarily by the fact that it is a pervious or porous bodythat offers substantially less resistance to flow than a porouscomponent 61. The first pervious component 59 may be obtained by thesintering of metal particles having a size substantially larger thanthat used in the porous component 61. As will be obvious in producing acomposite structure with such different grades of particulate metal caremust be taken that the particles which are to form porous layer 61 donot pentrate and clog the interstices or void spaces in perviouscomponent 59 at the time of fabrication. This may, for example, beprevented by admixing to the powdered metal which is to form the coarsecomponent 59 a combustible or soluble substance, of the nature indicatedin previous embodiments, so that the mixture of the two will form avoidless layer upon the solid sheet metal member 60, Upon sintering ofthe composite, the three layers will be metallurgically bonded to eachother. If the void preserving substance in the pervious component 59 iscombustible, then it will burn up in the course of sinterings; and if itis soluble, it may be leached out after the sintering operation.

It is noted that the pervious component 59 may be applied uniformly overthe entire surface of the solid sheet metal component 60 and then inturn covered over its entire remaining exposed area with the porouscomponent 61. Alternately, the pervious component 59 may be applied in apredetermined manner, as shown in FIGURE 1, and the second porouscomponent 61 then applied thereover so that the second porous component61 will be partly in contact with the first pervious component 59 and inother areas with the solid sheet metal component 69. It will beunderstood that the pervious component 59 may be produced in many otherways, as indicated in the previous embodiments, and the above example isintended only to serve merely as an illustration. For example, one mayuse any structural member that permits comparatively free flow of fluidsin a cross-direction. Thus, one may fabricate strips of metal into acomplex maze and attach it to the solid sheet metal component 66 bybrazing. The second porous component 61 may be applied not only by themethods of powder metallurgy but also by casting or from wire mesh asindicated in the preceding embodiments, and the structures to beproduced from such composites may take numerous shapes, each embodimentresulting in a structure that contains a region of low resistance to theflow of fluids, termed a pervious layer, bounded on one side by animpervious body, such as a solid sheet of metal, and on the other sideby a porous layer having substantially higher resistance to flow. Forexample, the resistance to flow, as characterized by pressure dropacross the respective layer, may be twice to several hundred timesgreater in the porous layer than it is in the pervious layer.

If it is desired to provide a channel in place of the pervious body 59without deforming the solid metal component 60 as described in previousembodiments, then the body 59 above referred to as being made ofparticles producing coarse porosity may instead be made of a soluble orcombustible substance around which the porous body 61 is formed asbefore. Upon sintering the porous body 61 is rendered cohesive withinitself and is joined to the solid metal body 69, while the combustiblesubstance will have been removed in the course of sintering, or thesoluble substance, if used, remains in place during sintering but isremoved thereafter by leaching. In either event, a composite body isformed consisting of a solid metal body 60 and a porous layer 61 whichlayer contains channels left after removal of the evanescent substancewhich channels are entirely within the porous body.

As will be understood, the selection of materials from which the porousand solid components are made to comprise the structures describedherein and in the co-pending application, is based on considerationswithin the skill of persons acquainted with mechanical, physical andchemical properties of materials. While the structures described hereinhave been identified as being metallic on numerous occasions, it ispointed out that all or parts of these structures may be made ofnon-metallic materials, as called for by their intended use. Thus, theporous layer may incorporate catalysts, as pointed out in the co-pendingapplication, which catalysts may be non-metallic. The porous layer mayalso consist in part or entirely of glasses, carbides, nitrides, oxides,or borides, for example in instances calling for heat resistance,corrosion resistance or insulating properties not available in metalsand alloys. The porous layer may also consist of synthetic polymericsubstances, for similar reasons, as for example sintered porousfluoro-carbon resins, silicone resins, and others. The solid componentis usually made of metal strip or plate which may be coated withnon-metallic materials of the kind referred to. In instances not callingfor high strength the solid component may also be made of syntheticresins made into strip, sheet or plate stock.

Several of the embodiments described herein may be made advantageouslyof non-metallic components. Thus, a component intended to distributehighly corrosive inorganic acid vapors may be made of fluorocarbonresins; another intended to serve as diffuser of combustible gas alsoacting as a radiant burner may be made in part of silicone carbide,Other examples are obvious to those skilled. in the art of constructingcomponents to be used in environments of high temperature and corrosiveattack.

It will be understood that the porous layer referred to herein may beproduced in still additional ways either in situ, upon the surface of asolid component or separately, to be joined thereto. Thus, the porouscomponent may be produced by mechanical perforation of a solid metallicsheet, however, such a method would generally be expensive andcumbersome. The porous layer may also be produced by spraying of metalby techniques Well-known to those skilled in the metal working art andcarried out either with a wire gun or a powder gun, whereby throughappropriate and well-known adjustment of the spray gun, the sprayingprocess may be directed so as to produce a porous sprayed deposit. Aporous sprayed deposit may also be produced with a powder gun byspraying along with the material intended to form the porous layer andintimately intermingled with it an evanescent solid which will bedeposited along with the rest of the sprayed material and which may thenbe removed from the porous composite by leaching as described inprevious examples. However, this procedure of producing the porous layerby spraying is also cumbersome and expensive in most instances, comparedto the other means described herein and in the co-pending applications.

In a modification shown in FIGURES 2 to 5, the preceding embodiments maybe fabricated so as to adapt them to be provided with a manifold orheader integral with the composite structure. In such a modification theporous component or components are provided on a face of a solid sheetmetal component so as to dispose them in spaced relationship with thesolid component. In this manner, the porous overlay does not extend overthe full length or width of the solid sheet metal component so that anuncovered portion 62 is provided with dimensions appropriate to thepurpose to be described below. Before or after the sintering operationnecessary to attach the porous component to the solid component theuncovered portion 62 of the solid sheet member 60 is appropriately slitat 63 and blanked to adapt it to the formation of a manifold or header64. Upon bending, tab portions 65 and 66 of the solid sheet metal memberare folded over to form respective end Walls 67 and 68 of the manifoldor header 64. If desired the manifold structure may also be providedwith a tab 69 disposed so as to cover a small portion of the externalface of the porous composite. After bending of the solid component intomanifold or header 64 and locating tab 60 in face-to-face relationshipwith the porous body, tab 69 may be welded to the porous body, or if theassembly is made before the heating operation, the tab may be integratedby metallurgical bonding during the sintering operation. Subsequent tothe integration of the porous body, the header or manifold 64 may beadapted for the introduction of a fluid by the insertion of a conduit 70within an opening 71 formed in an inwall, such as 68, of the manifold.

FIGURES 6 and 7 represent a still further modification of thisembodiment wherein the fluid channels of the integrated compositeassembly disposed between the porous component 72 and the solid sheetmetal component 73 are formed by deformation or distention of portionsof the solid sheet metal component 73 away from the porous component soas to form groove-like indentations 74 corresponding to the desiredfluid channels 75.

FIGURE 8 shows a still further modification of this embodiment adaptedto place two fluids in heat exchange relationship with each other bymeans of the composite structure, one of the fluids being containedwithin a tubular structure 76 and the other within the channels and theporous layer of the composite structure. Tubular structure 76 may beformed from a trough-like structure comprised of a bottom wall 77 andside walls 78 having inwardly extending flanges 79 suitably secured bywelding, brazing, and the like, to the external face of the solid sheetmetal member 73. The resultant conduit 80 defined by the tubularstructure 76 confines the fluid contained therein in a desired heatexchange relationship with the fluid contained in the porous compositestructure of this embodiment.

FIGURE 9 illustrates a still further embodiment of this inventionadapting it to the provision of three fluid containing conduits. In thisembodiment a porous composite structure is formed comprised of asheet-like porous body 81 having superimposed and integrated to each ofits opposite faces a solid sheet metal member 82 having predeterminedportions thereof suitably deformed and distended into groove-likeindentations 83 defining fluid containing channels 84. In a mannersimilar to the preceding embodiment, a channel forming member 85 issecured to the external faces of each of the solid sheet metal members82.

As indicated above, the composite structures of this invention areadapted for many applications and particularly for use as heatexchangers. As is well known, tubular components used in heat exchangerswere heretofore usually provided with fins, corrugations and otherextensions of their surface so as to present an economic maximumextended surface area for a given weight of heat exchanger structure.However, such heat exchanger structures can be provided with greatlyincreased heat transfer surfaces by, i.e., heat conductive bonding of asolid sheet metal unit to a sheet-like layer of sintered porous metal inaccordance with any of the methods described heretofore. As has beendiscussed the sheet-like porous metal component is attached to the solidsheet metal unit by a metallic bond which will warrant good heattransfer with channels provided between the confronting faces of thecomponents by interrupting the metallurgical bond in predetermined areasand in a predetermined pattern. These channels serve to conduct a fluidbetween the solid and porous layers with subsequent dilfusion of flowthrough the porous body, thereby contacting the large surface areaWithin the porous body, as defined by the innumerable intersticesextending between the integrated particles of the porous body. Forexample for application in refrigerator systems, where the solid sheetmetal unit is internally laminated with its laminations distended into asystem of fluid passageways, the fluid contained within the solid metalcomponent may be water and the fluid contained within the channels maybe liquid refrigerant or refrigerant vapor, as would be the case whensuch composite structures are used as refrigeration condensers orevaporators.

What is claimed is:

1. A method of making a sheet-like porous metal structure comprisingmetallurgically bonding a first sintered porous body of metal to a firstportion of a face of an impervious sheet metal member, superimposing onsaid first porous body and On a second portion of said face a mass ofparticulate metal aggregate adapted to be sintered together to form asecond body of metal of relatively less porosity than said first porousbody, with said mass of metal aggregate being disposed on said sheet toembed said first body into said mass of metal aggregate, sintering saidmass of metal aggregate to metallurgically bond the contacting metalsurfaces of said aggregate to provide a second porous metal bodymetallurgically bonded to said first porous body and to said secondportion of said face, adapting said first porous body to receive a fluidtherein, and injecting said fluid under suflicient pressure into saidfirst porous body to cause said fluid to flow through said first andsaid second porous bodies.

2. A method of making a sheet-like porous metal structure comprisingforming a composite porous structure by embedding a first porous body ina second porous metal body of relatively less porosity with both saidfirst and said second bodies having exposed surfaces extending in acommon plane, superimposing said structure on a face of an imperforatemetal sheet with said common surfaces disposed in confrontingrelationship with said face, metallurgically bonding said compositestructure to said sheet at their interface, adapting said first porousbody to re ceive a fluid therein, and injecting said fluid undersuflicient pressure into said first porous body to cause said fluid toflow through said first and said second porous bodies.

References Cited UNITED STATES PATENTS 2,267,918 10/1941 Hildabolt29182.3 X 2,293,843 8/1942 Maruin.

2,300,048 10/1942 Koehring 29182.3 X 2,772,180 11/1956 Neel.

2,836,641 5/1958 Vogt 208 X 2,845,346 7/1958 Scanlon et al. 75-2082,946,681 7/1960 Probst et a1.

2,979,400 4/1961 Mouwen 29l82.2 X 3,138,009 6/1964 McCreight 75-222 X3,226,263 12/1965 OsWin 75-22 X 3,230,618 l/l966 Valyi 29-470.93,247,573 4/1966 Noack 29155.5

JOHN F. CAMPBELL, Primary Examiner. P. M. COHEN, Assistant Examiner.

